LU-8837 mgc: move server-only code out of mgc_request.c

LU-8837 mgc: move server-only code out of mgc_request.c

Create a new mgc_request_server.c to contain all the server-only code
from mgc_request.c.
Among other changes, this involves splitting
  mgc_process_recover_nodemap_log()
into two separate functions:
 mgc_process_recovery_log() for cld_is_recover() case
 mgc_process_nodemap_log() for cld_is_nodmap() case

This does add some code duplication, but removes a lot of repetitive
case checking.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I9b3795d6c8ea2c812b98a3388d687af1d7732e0a
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/41995
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>